Vehicles equipped with self-loading/unloading apparatus of the type including a movable flexible belt and an associated movable bulkhead are in general known as disclosed in my prior U.S. Pat. No. 3,498,482, issued Mar. 3, 1970.
Such apparatus have proved successful in reducing the time and labor needed to unload cargo from truck and trailer bodies, especially particulate and compactible cargo as sawdust, wood chips, humus, sand, gravel and garbage. As described in the above-mentioned U.S. patent, to unload these types of cargo it is advantageous, if not essential, to provide a lost motion coupling between the bulkhead and belt so that during unloading, the belt is moved aft (toward the discharge end of the body) approximately one to four feet before the bulkhead begins its aft travel, in order to decompact the cargo. Such decompaction relieves some of the frictional forces existing between the cargo and the sidewalls which, in turn, lessens the force required by the bulkhead to push the cargo toward the discharge end of the bed.
An optimum distance of travel of the belt relative to the bulkhead during the lost motion action, can be determined for each application. The distance will vary as a function of such factors as the type of cargo, the length of the bed and the height of the sidewalls. For some applications, a relatively large amount of belt travel is required such as in the embodiment of the invention disclosed in my prior U.S. patent. In such case, a lost motion mechanism employing a roller as disclosed therein has proven to be of advantage because the excess length of belt needed to accommodate the relatively long belt-to-bulkhead travel is wound into a compact coil on a roller assembly journaled on a support frame for the bulkhead.
In other applications, a lesser amount of belt-to-bulkhead lost motion travel is required and it is thus desirable to use a less complex, lower cost lost motion coupling. Also there are some applications that require a belt drive system which is incompatible with the use of a lost motion roller carried by the support frame of the bulkhead. For these reasons the use of a non-rotating, or translational lost motion coupling between the belt and bulkhead has been proposed. In such a coupling the support frame for the bulkhead is provided with forward and rear catch surfaces that are spaced apart in the direction of belt travel by the distance of belt-to-bulkhead travel that is required. During unloading, drive means attached to the belt moves in a horizontal plane from the forward catch surfaces to the rear catch surfaces on the bulkhead support frame allowing the belt to advance toward the aft or discharge end of the bed before the bulkhead commences to move aft. When the drive means contacts the rear catch surfaces on the bulkhead frame, the bulkhead is entrained along with the belt to complete the unloading operation. Thereafter, the belt and bulkhead are returned to their initial positions.
While the principle of this translational lost motion coupling is straight forward, its implementation has proved troublesome. One particular difficulty has been a tendency of the bulkhead to become cocked (rotated about a vertical axis) relative to the sidewalls, during the lost motion travel of the belt with respect to the bulkhead, whereupon the bulkhead binds against the sidewalls or side-rail guides. This usually occurs during the lost motion action when the drive means on the belt is out of contact with the catch surfaces on the support frame and there is no positive engagement therebetween to cause the bulkhead to align itself with the drive means.
The most straight-forward solutions to this problem of the binding of the bulkhead have not proved effective. For example, one might suspect that it would be easy to maintain alignment between the bulkhead and the belt by providing close tolerance tracks and sliders for guiding the bulkhead with respect to the body and thereby maintaining the bulkhead in constant alignment with the bed and thus with the sidewalls. However, close tolerance guiding of the bulkhead in this environment produces an undesirable frictional drag on the bulkhead that can severely overload the bulkhead drive force which is limited by the strength characteristics of the belt. Also, the environment of the apparatus is such that any closely fitting track and slider components tend to accumulate grit which increases both the frictional effects and the tendency of the bulkhead to bind up. Therefore, it has been found desirable to maintain a loose fit between the the bulkhead and the sidewalls of the body so as to minimize the frictional forces and provide greater immunity of the apparatus to the presence of sand, grit, dirt and other particulate matter. However, the loose fit of the bulkhead with respect to the sidewalls merely aggravates the tendency of the bulkhead to cock and thus bind.
Another operational problem attributed to the presence of sand, grit, dirt and other particulate matter, is a tendency of the lateral edges of the belt to become frayed due to the abrasive effects of accumulated grit and the like in belt-edge retaining recesses that are provided along the sidewalls of the body. This is especially true when hauling certain types of cargo, such as gravel or sand, which due to vibration occurring during transport, will tend to work into the recesses. Also, some of the sand or gravel will work under the belt and degrade or destroy an antifriction sheet over which the lower surface of the belt slides.
Accordingly, one object of the invention is to provide a lost motion mechanism of the translational type for coupling the belt and bulkhead in a self-unloading apparatus of the above-described character, which maintains alignment between the bulkhead and the belt during the lost motion travel of the belt with respect to the bulkhead. More specifically, it is desired to eliminate the tendency of the bulkhead to bind against the sidewalls or sidewall guides of the truck or trailer body due to cocking of the bulkhead and its support frame during the lost motion movement of the belt relative to the stationary bulkhead at the initiation of each unloading operation.
A further object of the invention is to provide an improved self-unloading apparatus of the character described which is less susceptible to malfunction and rapid wear due to grit, sand, gravel or other particulate matter that constitutes or accompanies the cargo carried by such trucks or trailers.
Another object of the present invention is to provide an improved self-unloading apparatus of the above-described character which prevents the edges of the belt from rapidly becoming frayed due to the abrasive effects of accumulated grit and other particulate matter adjacent the edges of the belt. A related object is to prevent grit and other particulate matter from accumulating beneath the belt and abrading the smooth, low friction surface over which the lower surface of the belt slides.